Growth-related changes in specific mRNAs of cultured mouse cells

Control of proliferin gene expression in serum-stimulated mouse cells

The serum-inducible expression of proliferin genes in BALB/c 3T3 cells was found to be dependent on both protein synthesis and an extended presence of serum in the medium. Even though no mature proliferin mRNA was detected in serum-starved cells, transcription of the proliferin genes occurred in these resting-cell cultures, indicating that posttranscriptional events may be important for regulating proliferin mRNA levels. These results suggest that protein synthesis after serum stimulation of quiescent mouse fibroblasts is required for posttranscriptional processing or stabilization of proliferin RNA. Proliferin RNA levels were found to be heterogeneous among serum-stimulated cells analyzed by in situ hybridization. This heterogeneity is probably due to asynchrony in the population and may point to a correlation between the time of proliferin expression and the time of entry of a cell into S phase.

Expression of growth-associated genes in various tissues of the fetal and adult rat

4F1, 2A9 and 2F1 represent three of a number of cDNA sequences which have been identified because their cognate RNAs markedly increase when quiescent cells in culture are stimulated with serum. Studies using a variety of cell culture systems have shown that the expression of these genes is modulated by various growth factors and mitogens and thus such genes are considered to be 'growth-associated.' Thus far, little information has been obtained with these in vitro systems about the function of these genes. In an attempt to begin to elucidate the role of these genes (if any) in the physiology of the normal cell, we have analyzed the levels of 4F1, 2A9 and 2F1 transcripts in a variety of differentiated organs and tissues of adult and fetal rats. Our results show that each of these growth-associated genes exhibits its own unique pattern of expression, unrelated to the proliferative activity of the tissue. These data suggest that these genes most likely do have specific functions in normal tissue in addition to their role in the induction of DNA synthesis in quiescent cells in culture.

Expression of a set of growth-related immediate early genes in BALB/c 3T3 cells: coordinate regulation with c-fos or c-myc

We have previously identified by cDNA cloning 5 mRNAs that appear in resting BALB/c 3T3 cells soon after growth stimulation by serum or platelet-derived growth factor. Five additional mRNAs of this class are described in this report. The mRNAs reached peak levels between 40 and 120 min after serum addition and rapidly decayed thereafter. All 10 RNAs were superinduced in the presence of cycloheximide. Nuclear run-on experiments indicated that the increase in the mRNAs is the result of rapid transcriptional activation of their genes on stimulation by serum or platelet-derived growth factor. Superinducibility by cycloheximide is due to two effects: prolonged transcription and stabilization of mRNAs. This overall pattern of regulation is similar to that of the c-fos or c-myc protooncogenes reported previously. We hypothesize that these newly identified "immediate early" genes play a role in the proliferative response induced by growth factors.

Isolation of an olfactory cDNA: similarity to retinol-binding protein suggests a role in olfaction

Molecular cloning techniques were used to isolate and characterize a protein possibly involved in the signal transducing system in olfactory tissue of the frog Rana pipiens. A complementary DNA library was constructed with messenger RNA obtained from frog olfactory neuroepithelium. A 700-base pair complementary DNA clone encoding a protein with a molecular weight of 20,300 was identified by differential hybridization analysis with polyadenylated RNA from olfactory epithelium and nonsensory respiratory epithelium. The messenger RNA corresponding to this clone was abundant in the cells of Bowman's glands in olfactory tissue but not in respiratory epithelium nor in several other tissues. The predicted sequence of this protein is homologous to members of a family of proteins that bind and transport small molecules in serum, suggesting that this protein may also bind and transport odorants in the mucus secreted by Bowman's glands.

The human growth hormone gene locus: structure, evolution, and allelic variations

Genomic clones containing the closely related genes for human growth hormone (hGH) and chorionic somatomammotropin (hCS) were obtained from genomic bacteriophage lambda and cosmid libraries. The entire GH/CS chromosomal locus was reconstructed utilizing overlapping restriction fragments characterized from the isolated clones. The hGH/hCS locus contains two GH genes and three CS genes spanning 48 kb of DNA in the order: 5'-(hGH-1/hCS-5/hCS-1/hGH-2/hCS-2)-3', confirming analysis of cosmid clones obtained from a different human library (Barsh et al., 1983). To complete the characterization of the hCS genes, the nucleotide sequence of the hCS-5 gene was determined. Sequence analysis revealed a mutation of the 5' splice site at the exon II-intron B boundary, suggesting that the hCS-5 gene is a pseudogene. The nucleotide sequence of an allelic variant of the hCS-2 gene was determined and found to contain a single amino acid substitution and the deletion of a single codon. The hGH/hCS gene locus was further characterized by the localization of at least 27 Alu-type repetitive sequences and identification of three unique sequences in the vicinity of several hGH and hCS genes which define the probable breakpoints of the evolutionary duplication units. These data, combined with the nucleotide sequences of all five GH and CS genes, indicate that the hGH/hCS gene locus has evolved by duplication mechanisms. Evidence for the occurrence of at least one gene conversion event involving the hCS-1 gene precursor and the hCS-2 gene was found, indicating that the hGH/hCS gene locus has evolved by concerted mechanisms. The structure of the hCS genes is discussed in light of recent studies of CS genes from other mammalian species.

Induction of metallothionein and other mRNA species by carcinogens and tumor promoters in primary human skin fibroblasts

We used nucleic acid hybridization and cDNA cloning techniques to isolate human sequences that respond to the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). These clones were used as probes to examine changes of gene expression that occurred after the proliferation of exponentially growing primary human fibroblasts was arrested. Transcript levels detected by these probes were increased coordinately by treatment of the cells with UV light, mitomycin C, TPA, or the UV light-induced extracellular protein synthesis-inducing factor EPIF (M. Schorpp, U. Mallick, H. J. Rahmsdorf, and P. Herrlich, Cell 37:861-868, 1984). Proteins coded for by these transcripts were characterized by hybrid-promoted translation and by cDNA sequencing. One of the cDNA clones was homologous to the metallothionein IIa gene, and one set of related clones selected RNA for the secreted TPA-inducible protein XHF1 (U. Mallick, H. J. Rahmsdorf, N. Yamamoto, H. Ponta, R.-D. Wegner, and P. Herrlich, Proc. Natl. Acad. Sci. USA 79:7886-7890, 1982).

Expression of multiple proliferin genes in mouse cells

Several copies of the prolactin-related proliferin gene were detected in the mouse genome, encoding at least two distinct forms of proliferin. These forms correspond to proliferin cDNA clones derived from BALB/c 3T3 tissue culture and BALB/c placental RNA. Tissue culture and placental cells were each found to express both forms of proliferin.

A growth-responsive gene (16C8) in normal mouse fibroblasts homologous to a human collagenase inhibitor with erythroid-potentiating activity: evidence for inducible and constitutive transcripts

We present the DNA sequence of an essentially full-length cDNA clone of 16C8, a growth factor-inducible gene isolated from a mouse embryo fibroblast cDNA library. The 0.9-kb mRNA encodes an Mr 22,500 protein that has substantial homology to a human protein with the reported abilities to potentiate erythroid differentiation and to inhibit collagenases and other tissue metalloproteinases. The N-terminus of the predicted protein has a hydrophobic nature characteristic of secreted proteins, and two potential sites for N-linked glycosylation are present. The cytoplasmic concentration of 16C8 mRNA is maximal in mid G1 at about 6 h after serum stimulation of quiescent fibroblasts. Northern blot analysis showed a progressive reduction in the size of the induced 16C8 transcripts with increasing time after serum stimulation. This was shown to be due to the reduction in length of the poly(A) tails. S1 analysis of the 5' portion of the mRNA revealed the presence of three different species of transcript, only one of which was inducible.

Expression of growth-regulated genes in tsJT60 cells, a temperature-sensitive mutant of the cell cycle

We have investigated the expression of growth-regulated genes in tsJT60 cells, a temperature-sensitive (ts) mutant of Fischer rat cells, which, on the basis of its kinetic behavior, can be classified as a G0 mutant. It grows normally at 34 degrees C and also at 39.5 degrees C if shifted to the higher temperature during exponential growth. However, if the cell population is first made quiescent by serum deprivation, subsequent stimulation by serum induces the cells to enter S phase at 34 degrees C but not at 39.5 degrees C. A panel of growth-regulated genes was used that included three protooncogenes (c-fos, c-myc, and p53), several genes that are induced in G0 cells stimulated by growth factors (beta-actin, 2A9, 2F1, vimentin, JE-3, KC-1, and ornithine decarboxylase), and an S-phase gene (histone H3). The expression of these growth-regulated genes was studied in both tsJT60 cells and its parental cell line, rat 3Y1 cells. All the genes tested, except histone H3, are similarly induced when quiescent tsJT60 cells are stimulated by serum at either permissive or restrictive temperatures. These results raise intriguing questions on the nature of quiescence and the relationship between G0 and G1 in cells in culture.

Molecular cloning of mouse placental lactogen cDNA

We have isolated a cDNA clone for the 23-kDa mouse placental lactogen II (mPL-II) from a phage lambda gt11 expression library containing cDNA synthesized from BALB/c placental RNA. Translation in vitro of placental mRNA selected by hybridization to the mPL-II cDNA clones yields a 26-kDa polypeptide that is the size of the expected precursor protein and that is immunoprecipitated with anti-mPL-II antiserum. The mPL-II cDNA clones hybridize to a 1.0-kilobase placental-specific mRNA. This mRNA, found in the fetal portion of the placenta, appears as early as day 10 of gestation and increases to a maximal level by day 12. The mPL-II cDNA nucleotide sequence has been determined. This sequence contains an open reading frame encoding a polypeptide of 222 amino acids with the amino-terminal 31 amino acids forming the signal sequence for secretion. The predicted secreted protein has 51% amino acid homology with mouse prolactin.

Adenovirus type 2 activates cell cycle-dependent genes that are a subset of those activated by serum

We have studied a panel of 10 genes and cDNA sequences that are expressed in a cell cycle-dependent manner in different types of cells from different species and that are inducible by different mitogens. These include five sequences (c-myc, 4F1, 2F1, 2A9, and KC-1) that are preferentially expressed in the early part of the G1 phase, three genes (ornithine decarboxylase, p53, and c-rasHa) preferentially expressed in middle or late G1, and two genes (thymidine kinase and histone H3) preferentially expressed in the S phase of the cell cycle. We have studied the expression of these genes in nonpermissive (tsAF8) and semipermissive (Swiss 3T3) cells infected with adenovirus type 2. Under the conditions of these experiments, adenovirus type 2 infection stimulates cellular DNA synthesis in both tsAF8 and 3T3 cells. However, four of the five early G1 genes (c-myc, 4F1, KC-1, and 2A9) and one of the late G1 genes (c-ras) are not induced by adenovirus infection, although they are strongly induced by serum. The other sequences (2F1, ornithine decarboxylase, p53, thymidine kinase, and histone H3) are activated by both adenovirus and serum. We conclude that the cell cycle-dependent genes activated by adenovirus 2 are a subset of the cell cycle-dependent genes activated by serum. The data suggest that the mechanisms by which serum and adenovirus induce cellular DNA synthesis are not identical.

Transcriptional regulation of two serum-induced RNAs in mouse fibroblasts: equivalence of one species to B2 repetitive elements

We obtained eight cDNA clones that define five genes whose expression (appearance of transcripts in the cytoplasm) is enhanced when quiescent mouse fibroblasts are stimulated with serum to divide. Two of these clones (designated 49C8 and 16C8) correspond to RNA species that are present in the cytoplasm of quiescent cells at very low levels. After serum stimulation, the level of 16C8 mRNA rose more rapidly than that of 49C8 RNA, reaching a maximum around 6 to 12 h. The data suggest that 49C8 and 16C8 RNAs are induced as a result of independent stimuli. Either fibroblast growth factor or 12-tetradecanoylphorbol-13-acetate alone could induce 16C8 expression almost as effectively as serum; in contrast, 49C8 was not efficiently induced by epidermal growth factor, fibroblast growth factor, insulin, or 12-tetradecanoylphorbol-13-acetate. Inhibitors of transcription and translation diminished the induction of 16C8, while 49C8 expression was sensitive to actinomycin D but not cycloheximide or 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole. In vitro transcription experiments with isolated nuclei revealed a peak in transcriptional activity of the 16C8 gene at around 3 h after serum stimulation. Sequence analysis of the 49C8 cDNA clone showed greater than 90% homology of a large portion to a consensus rodent B2 repetitive element.

Characterization of a cDNA clone encoding murine mitogen-regulated protein: regulation of mRNA levels in mortal and immortal cell lines

Mitogen-regulated protein (MRP) is secreted by certain immortal murine cell lines (Swiss 3T3, BNL) stimulated with serum or particular growth factors. We have identified a cDNA clone that encodes part of the protein and have confirmed that MRP is closely related to, if not identical to, the prolactin-related protein designated proliferin. MRP is not produced by primary mouse embryo fibroblasts to nearly the same extent as it is produced by many immortal or transformed lines. Control of expression of this protein by growth factors is achieved both by regulating the extent of transcription and by regulating the processing of the protein.

Regulation of the transcript for a lysosomal protein: evidence for a gene program modified by platelet-derived growth factor

Platelet-derived growth factor (PDGF) stimulates density-arrested BALB/c-3T3 cells to synthesize MEP, a lysosomal protein. This enhanced synthesis appears to be largely regulated by the PDGF-modulated accumulation of MEP mRNA, a 1.8-kilobase species. The increase in the MEP transcript, which is dependent on the PDGF concentration, begins 3 to 4 h after PDGF addition and is maximal at 12 h. The accumulation of the MEP transcript is growth-factor specific: PDGF and the tumor promoter 12-O-tetradecanoylphorbol-13-acetate, an agent which acts like PDGF, induce MEP RNA accumulation, whereas epidermal growth factor, somatomedin C, insulin, and whole plasma do not. A spontaneously transformed BALB/c-3T3 cell line (ST2-3T3), which does not require PDGF for growth, optimally expresses MEP RNA in the absence of PDGF. The PDGF-modulated increase in MEP RNA is unlike PDGF-modulated c-myc and c-fos RNA accumulation because it is blocked by cycloheximide, suggesting a requirement for de novo protein synthesis. It appears that PDGF modulates a program of gene expression with the accumulation of some transcripts, typified by MEP, being dependent upon the translation of others.

Expression of multiple proliferin genes in mouse cells

Several copies of the prolactin-related proliferin gene were detected in the mouse genome, encoding at least two distinct forms of proliferin. These forms correspond to proliferin cDNA clones derived from BALB/c 3T3 tissue culture and BALB/c placental RNA. Tissue culture and placental cells were each found to express both forms of proliferin.

Cell cycle dependent genes inducible by different mitogens in cells from different species

A number of genes and cDNA sequences (including at least four oncogenes) are known to be expressed in a cell cycle-dependent manner, i.e. the levels of specific mRNAs vary with the phases of the cell cycle. In order to explore the significance of some of these sequences in the mitogenic response, we have investigated the expression of 8 cell cycle-dependent sequences (plus two control sequences, not expressed in a cell cycle-dependent manner) under a variety of conditions. These conditions included cells of different types, from different species, stimulated to proliferate by different mitogens. The genes (or sequences) studied included five cDNA clones whose sequences are preferentially expressed in early G1, i.e. two cDNA clones inducible by platelet-derived growth factor (JE-3 and KC-1), and three cDNA clones inducible by serum (2A9, 2F1, 4F1); and three oncogenes (c-myc, c-rasHa and p53) whose expression is known to be cycle-dependent. All of the tested genes, except 2A9, c-rasHa and the control genes, are expressed in a cell cycle-dependent manner in human peripheral blood mononuclear cells stimulated by phytohemagglutinin and in serum-stimulated mouse and Syrian hamster fibroblasts. The inducibility of these genes by different mitogens in cells of different types and from different species strongly suggests that these genes play a role in cell cycle progression. This conclusion is further supported by the known structural and functional similarities between cell-cycle dependent genes, oncogenes and genes coding for cell-cycle related molecules.

Replication and transformation functions of in vitro-generated simian virus 40 large T antigen mutants

We used sodium bisulfite mutagenesis to introduce point mutations within the early region of the simian virus 40 genome. Seventeen mutants which contained amino acid changes in the amino-terminal half of the large T antigen coding sequence were assayed for their ability to replicate viral DNA and to induce transformation in the established rodent cell line Rat-3. The mutants fell into four basic classes with respect to these two biological functions. Five mutants had wild-type replication and transformation activities, six were totally defective, three were replication deficient and transformation competent, and two were replication competent and transformation deficient. Within these classes were mutants which displayed intermediate phenotypes, such as four mutants which were not totally deficient in viral replication or cellular transformation but instead showed reduced large T antigen function relative to wild type. Three large T mutants displayed transforming activity that was greater than that of wild type and are called supertransforming mutants. Of the most interest are mutants differentially defective in replication and transformation activities. These results both support and extend previous findings that two important biological functions of large T antigen can be genetically separated.

Expression of cell cycle-dependent genes in young and senescent WI-38 fibroblasts

We studied the expression of 11 cell cycle-dependent genes in senescent WI-38 fibroblasts and compared the results to those obtained in WI-38 cells from early passages (young cells). Every gene we examined is expressed in the senescent cells at levels similar to those in the young cells, including two genes maximally expressed at the G1/S phase boundary--genes for thymidine kinase and histone H3. The results clearly show that senescent, noncycling WI-38 cells are not similar to quiescent cells. Rather, such senescent WI-38 cells may be blocked just prior to the onset of DNA synthesis.

Induction of metallothionein and other mRNA species by carcinogens and tumor promoters in primary human skin fibroblasts

We used nucleic acid hybridization and cDNA cloning techniques to isolate human sequences that respond to the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). These clones were used as probes to examine changes of gene expression that occurred after the proliferation of exponentially growing primary human fibroblasts was arrested. Transcript levels detected by these probes were increased coordinately by treatment of the cells with UV light, mitomycin C, TPA, or the UV light-induced extracellular protein synthesis-inducing factor EPIF (M. Schorpp, U. Mallick, H. J. Rahmsdorf, and P. Herrlich, Cell 37:861-868, 1984). Proteins coded for by these transcripts were characterized by hybrid-promoted translation and by cDNA sequencing. One of the cDNA clones was homologous to the metallothionein IIa gene, and one set of related clones selected RNA for the secreted TPA-inducible protein XHF1 (U. Mallick, H. J. Rahmsdorf, N. Yamamoto, H. Ponta, R.-D. Wegner, and P. Herrlich, Proc. Natl. Acad. Sci. USA 79:7886-7890, 1982).

Transforming growth factor type beta regulation of actin mRNA

Stimulation of quiescent cultures of AKR-2B cells with transforming growth factor type beta (TGF beta) resulted in a transitory increase in actin cytoplasmic poly(A) + RNA. Levels of actin mRNA peaked approximately 4-8 hours subsequent to TGF beta addition and approached basal levels by 24 hours. The accumulation of actin transcripts was dose dependent and insensitive to inhibitors of protein synthesis; 1-3 ng/ml TGF beta induced maximal actin gene expression. Actin isotype-specific probes demonstrated that both beta- and gamma-cytoplasmic actins are induced by TGF beta.

Molecular biology of the cell cycle

Genes and cDNA clones have been identified in animal cells that are cell cycle-regulated, i.e. they are preferentially expressed in a phase of the cell cycle. Some of these genes, including four oncogenes, are induced when G0 cells are stimulated to proliferate. Four approaches are described to identify the genes that regulate the transition of cells from a resting to a growing stage. The interrelationship among cell cycle-regulated genes, oncogenes, growth factors and receptors for growth factors points the way to a genetic dissection of cell cycle progression.

Hydrogen peroxide toxicity may be enhanced by heat shock gene induction in Drosophila

Recent evidence suggests that low dose exposure of cells to hydrogen peroxide and/or induction of heat shock protein (HSP) synthesis will render cells resistant to the lethal effects of a subsequent high dose hydrogen peroxide stress. We explored this possibility in the Drosophila melanogaster Schneider tissue culture line 2. It was found that chronic low dose exposure (1 mM H2O2 for 3 days) resulted in marked potentiation of the toxic effects of a subsequent high dose exposure (50 mM H2O2 for 1 h), as assessed by impairment of uridine incorporation and cell proliferation. Cells preexposed to low dose H2O2 exhibited enhanced heat shock gene transcription upon exposure to high dose H2O2, as compared to cells that did not receive low dose preexposure. Transcriptional induction of the heat shock genes by a mild non-toxic heat shock resulted in marked enhancement of the anti-proliferative effects of a subsequent H2O2 exposure. Thus, low dose hydrogen peroxide exposure or mild heating results in subsequent enhancement of high dose hydrogen peroxide toxicity; this effect correlates with enhanced heat shock gene expression. Possible mechanisms are discussed.

Identification of a set of genes expressed during the G0/G1 transition of cultured mouse cells

To identify previously undetected genes that may be involved in the transition from a resting state (G0) to a proliferative state (G1) of mammalian cells, we set out to isolate cDNA clones derived from mRNAs that appear in serum-stimulated cells in the absence of protein synthesis. A lambda cDNA library was prepared using poly(A)+ RNA from BALB/c 3T3 cells that had been brought to quiescence and subsequently stimulated with serum in the presence of cycloheximide. Approximately 50 000 recombinant phage plaques were screened, and 357 clones were isolated that hybridized to probes derived from stimulated-cell RNA but not to probes from resting-cell RNA. Cross hybridization analysis showed that four RNA sequence families account for approximately 90% of these clones. One of the clones hybridized to an actin probe; none hybridized to any of 13 oncogene probes tested. Five different RNAs that appear to be previously uncharacterized have been further analyzed. These RNAs accumulate and decay rapidly following stimulation by serum or purified growth factors, or by a tumor promoter, and they are superinduced by serum in the presence of cycloheximide. Three of the RNAs could be enriched by hybridization to cDNAs and translated in vitro, yielding proteins of approximately 43, 40 and 35 kd, respectively.

Characterization of a cDNA clone encoding murine mitogen-regulated protein: regulation of mRNA levels in mortal and immortal cell lines

Mitogen-regulated protein (MRP) is secreted by certain immortal murine cell lines (Swiss 3T3, BNL) stimulated with serum or particular growth factors. We have identified a cDNA clone that encodes part of the protein and have confirmed that MRP is closely related to, if not identical to, the prolactin-related protein designated proliferin. MRP is not produced by primary mouse embryo fibroblasts to nearly the same extent as it is produced by many immortal or transformed lines. Control of expression of this protein by growth factors is achieved both by regulating the extent of transcription and by regulating the processing of the protein.

Transcriptional regulation of two serum-induced RNAs in mouse fibroblasts: equivalence of one species to B2 repetitive elements

We obtained eight cDNA clones that define five genes whose expression (appearance of transcripts in the cytoplasm) is enhanced when quiescent mouse fibroblasts are stimulated with serum to divide. Two of these clones (designated 49C8 and 16C8) correspond to RNA species that are present in the cytoplasm of quiescent cells at very low levels. After serum stimulation, the level of 16C8 mRNA rose more rapidly than that of 49C8 RNA, reaching a maximum around 6 to 12 h. The data suggest that 49C8 and 16C8 RNAs are induced as a result of independent stimuli. Either fibroblast growth factor or 12-tetradecanoylphorbol-13-acetate alone could induce 16C8 expression almost as effectively as serum; in contrast, 49C8 was not efficiently induced by epidermal growth factor, fibroblast growth factor, insulin, or 12-tetradecanoylphorbol-13-acetate. Inhibitors of transcription and translation diminished the induction of 16C8, while 49C8 expression was sensitive to actinomycin D but not cycloheximide or 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole. In vitro transcription experiments with isolated nuclei revealed a peak in transcriptional activity of the 16C8 gene at around 3 h after serum stimulation. Sequence analysis of the 49C8 cDNA clone showed greater than 90% homology of a large portion to a consensus rodent B2 repetitive element.

Adenovirus type 2 activates cell cycle-dependent genes that are a subset of those activated by serum

We have studied a panel of 10 genes and cDNA sequences that are expressed in a cell cycle-dependent manner in different types of cells from different species and that are inducible by different mitogens. These include five sequences (c-myc, 4F1, 2F1, 2A9, and KC-1) that are preferentially expressed in the early part of the G1 phase, three genes (ornithine decarboxylase, p53, and c-rasHa) preferentially expressed in middle or late G1, and two genes (thymidine kinase and histone H3) preferentially expressed in the S phase of the cell cycle. We have studied the expression of these genes in nonpermissive (tsAF8) and semipermissive (Swiss 3T3) cells infected with adenovirus type 2. Under the conditions of these experiments, adenovirus type 2 infection stimulates cellular DNA synthesis in both tsAF8 and 3T3 cells. However, four of the five early G1 genes (c-myc, 4F1, KC-1, and 2A9) and one of the late G1 genes (c-ras) are not induced by adenovirus infection, although they are strongly induced by serum. The other sequences (2F1, ornithine decarboxylase, p53, thymidine kinase, and histone H3) are activated by both adenovirus and serum. We conclude that the cell cycle-dependent genes activated by adenovirus 2 are a subset of the cell cycle-dependent genes activated by serum. The data suggest that the mechanisms by which serum and adenovirus induce cellular DNA synthesis are not identical.

Growth-related changes in specific mRNAs upon lectin activation of human lymphocytes

A cDNA library in lambda gt10 was constructed from the cytoplasmic poly(A) +RNA of human peripheral blood lymphocytes after 72 hr of phytohemagglutinin stimulation, with the aim of assessing selective gene expression as a result of lymphocyte activation. Thirteen recombinants were isolated by the use of an enriched probe and differential screening. These clones were categorized into two groups with respect to their hybridization to mRNA. In the first group three recombinants were isolated, which hybridized to single discrete mRNAs in the size range 0.7-1.7 kb. The mRNAs corresponding to these clones were present at elevated levels in activated lymphocytes, but the kinetics of increase differed. The 0.7-kb mRNA coded for by clone p1L1 increased two-fold at 6 hr and remained elevated over 72 hr, as did beta-actin mRNA. The 1.7-kb mRNA coded for by clone p9L2 increased two- to three-fold after 6 hr and was maximally expressed after 24 hr exposure to phytohemagglutinin, coincident with the onset of DNA replication, and maintained this level up to 72 hr. The 1.0-kb mRNA coded by p10L2F which was rare in resting cells increased 25- to 30-fold after 6 hr, prior to overall transcriptional increases and reached peak levels after 72 hr when a substantial proportion of the cells were in the S and G2 + M phases of the cell cycle. This clone was undetectable or very rare in the leukemic T-lymphoblast cell line CCRF-CEM. The second group of clones, consisting of the remaining 10 recombinants, did not hybridize to discrete bands, but to a smear on RNA blots.(ABSTRACT TRUNCATED AT 250 WORDS)

A pBR322-derived vector for cloning blunt-ended cDNA: its use to detect molecular clones of low-abundance mRNAs

In place of the unique Pst I site in pBR322, we have engineered by GC tailing a unique Sma I site bracketed by Pst I sites. The resulting vector, pDE61, and an improved derivative with greater symmetry around the Sma I site, pDE613, have been used to clone blunt-ended duplex cDNA molecules in Escherichia coli in an efficient manner (5 X 10(5) clones from 1 microgram of double-stranded cDNA). When DNA is cloned into the Sma I site, the ability of both vectors to confer ampicillin resistance is lost. Evidence suggests that functional beta-lactamase is made only after the GC-rich sequence containing the Sma I site is deleted: an insert in the Sma I site prevents this. Libraries in either vector, with single or multiple inserts, can be used to generate amplified amounts of cloned heterogeneous cDNA for screening other "target" libraries in a non-homologous vector (e.g., a Bacillus subtilis vector) for cDNA clones of low-abundance mRNAs. Species as infrequent as 0.003% can be readily detected by colony hybridization.

Regulation of the transcript for a lysosomal protein: evidence for a gene program modified by platelet-derived growth factor

Platelet-derived growth factor (PDGF) stimulates density-arrested BALB/c-3T3 cells to synthesize MEP, a lysosomal protein. This enhanced synthesis appears to be largely regulated by the PDGF-modulated accumulation of MEP mRNA, a 1.8-kilobase species. The increase in the MEP transcript, which is dependent on the PDGF concentration, begins 3 to 4 h after PDGF addition and is maximal at 12 h. The accumulation of the MEP transcript is growth-factor specific: PDGF and the tumor promoter 12-O-tetradecanoylphorbol-13-acetate, an agent which acts like PDGF, induce MEP RNA accumulation, whereas epidermal growth factor, somatomedin C, insulin, and whole plasma do not. A spontaneously transformed BALB/c-3T3 cell line (ST2-3T3), which does not require PDGF for growth, optimally expresses MEP RNA in the absence of PDGF. The PDGF-modulated increase in MEP RNA is unlike PDGF-modulated c-myc and c-fos RNA accumulation because it is blocked by cycloheximide, suggesting a requirement for de novo protein synthesis. It appears that PDGF modulates a program of gene expression with the accumulation of some transcripts, typified by MEP, being dependent upon the translation of others.

Expression of cell-cycle-dependent genes in phytohemagglutinin-stimulated human lymphocytes

We have investigated the expression of certain cell-cycle-dependent genes in human peripheral blood mononuclear cells (PBMC) stimulated by phytohemagglutinin (PHA). The genes studied had been previously identified as cell-cycle dependent in other cell types from different species and were induced by different mitogens. One of these genes (2F1) and the gene for the interleukin 2 receptor were induced by PHA even in cultures partially depleted of accessory cells where the lymphocytes grew in size but failed to enter S phase. The other genes (c-myc, 4F1, JE-3, and KC-1) were induced only in complete cultures of PBMC stimulated by PHA. These results confirm the dissociation between growth in size and cell DNA replication that can occur during cell-cycle progression. Moreover, the time course of appearance of detectable levels of RNA for these genes suggests that they may be used as markers of cell-cycle progression in the transition of lymphocytes from G0 to S phase.

Cell-cycle-specific genes differentially expressed in human leukemias

Three cDNA clones isolated from Syrian hamster cells (p4F1, p2F1, and p2A9) contain sequences that are preferentially expressed in the G1 phase of the cell cycle. The expression of these sequences was investigated in human peripheral blood cells from normal individuals and from patients with leukemia. The expression of p4F1 and p2F1 is clearly dependent on the cell cycle in peripheral blood mononuclear cells stimulated to proliferate with phytohemagglutinin; the p2A9 sequences cannot be clearly detected in human lymphocytes but are expressed in a cell-cycle-dependent manner in human diploid fibroblasts (WI-38). These genes also show different levels of expression in lymphoid and myeloid leukemias. The highest level of expression for p2A9 is found in patients with chronic myelogenous leukemia, and the lowest in patients with chronic lymphocytic leukemia. For p2F1 and p4F1, the highest levels of expression are found in chronic and acute myelogenous leukemia. At least two other cell-cycle genes are not expressed at detectable levels in human leukemias. These findings suggest that the activation of cell-division-cycle genes might contribute, like cellular oncogenes, to the phenotype of human malignancies and that, perhaps, new oncogenes could be found by identifying and isolating genes whose expression is dependent on the cell cycle.

Similar action of platelet-derived growth factor and epidermal growth factor in the prereplicative phase of human fibroblasts suggests a common intracellular pathway

We have investigated the effects of platelet-derived growth factor (PDGF) and epidermal growth factor (EGF) in the prereplicative phase of human foreskin fibroblasts cultured under defined conditions in serum-free MCDB 105 medium. Specific antisera against PDGF and EGF were used to inhibit the stimulation after certain incubation times. It was found that PDGF or EGF had to be present during the major part of the G0/G1 phase (greater than 8 h) in order to cause any appreciable commitment to DNA synthesis; half maximal stimulations were obtained after 9 h and 11 h of incubations with PDGF and EGF, respectively. When tested during a suboptimal period of time (6 h), neither an increase in concentration of PDGF or EGF, nor the addition of both growth factors simultaneously caused any appreciable stimulation of DNA synthesis. However, a suboptimal pulse of PDGF, followed by a suboptimal pulse of EGF, or vice versa, led to commitment to DNA synthesis. This finding indicates that PDGF and EGF, at least in part, induce similar intracellular events that transmit the mitogenic signal.

RNAs containing B2 repeated sequences are transcribed in the early stages of mouse embryogenesis

An in situ hybridization technique was used to detect RNAs containing B2 sequences in the early mouse embryo. Accumulation of B2 sequences occurs early from the one cell stage. The level of B2 RNA decreases in the late two cell embryo, and then increases at the moment of second cleavage. In the blastocyst, inner cell mass cells contain more B2 transcripts than trophectoderm cells. In 7.5-day embryos the expression of B2 sequences is restricted to ectoderm and mesoderm. At all stages, transcription of the B2+ strand is greater than B2- strand. We detected B2+ RNAs in the nucleus and cytoplasm, whereas B2- RNAs were present only in the nucleus.

Identification of proliferin mRNA and protein in mouse placenta

Proliferin is a recently described, prolactin-related protein whose mRNA appears in several murine cell lines during active growth. We have surveyed a number of mouse organs or tissues for the presence of mRNAs that hybridize to cloned proliferin cDNA. Of the tissues tested, only the placenta yielded proliferin-related mRNA. This placental RNA is about 1 kilobase in length, increases sharply between days 8 and 10 of pregnancy, and then gradually declines through day 18. It is more abundant in RNA extracted from the fetal, compared to the maternal, part of the placenta. From a cDNA plasmid library prepared from poly(A)+ placental RNA, two types of proliferin-related clones were isolated, differing in intensity of hybridization to proliferin cDNA. By nucleotide sequence analysis, a strongly hybridizing clone was found to be nearly identical to the proliferin cDNA clone isolated from a library prepared from mRNA of a growing mouse fibroblastic cell line. Using an antiserum prepared against a synthetic proliferin fusion protein, we show that proliferin is secreted as a glycoprotein by minced placental tissue and that it differs from mouse placental lactogen. We conclude that proliferin is a placental hormone that is synthesized in certain mouse cell lines during active growth. Its function during pregnancy and during the growth of cultured cells is presently unknown.

Microinjected c-myc as a competence factor

While a number of oncogenes are expressed in a cell cycle-dependent manner, their role in the control of cell proliferation can only be established by a direct functional assay. The c-myc protein, upon microinjection into nuclei of quiescent Swiss 3T3 cells, cooperated with platelet-poor plasma in the stimulation of cellular DNA synthesis. This suggests that c-myc protein, like platelet-derived growth factor (PDGF), may act as a competence factor in the cell cycle to promote the progression of cells to S phase. The presence in the medium of an antibody against PDGF abolished DNA synthesis induced by microinjected PDGF; however, the microinjected c-myc protein stimulated DNA synthesis even when its own antibody was present in the medium. The c-myc protein may act as an intracellular competence factor, while PDGF expresses its biological activity only from outside the cells.

Expression of a mouse long terminal repeat is cell cycle-linked

The expression of the long terminal repeat (LTR) of intracisternal A particle retroviral sequences which are endogenous to the mouse genome has been shown to be linked to the early G1 phase of the cell cycle in Friend erythroleukemia cells synchronized by density arrest and also in logarithmically growing cells fractionated into cell-cycle compartments by centrifugal elutriation. Regions of homology were found in comparing the LTR sequence to a repetitive Syrian hamster sequence specifically expressed in early G1 in hamster cells.

Epidermal growth factor or serum stimulation of rat fibroblasts induces an elevation in mRNA levels for lactate dehydrogenase and other glycolytic enzymes

We have isolated cloned cDNAs corresponding to five mRNAs whose level is increased following stimulation of quiescent rat fibroblasts by either epidermal growth factor or serum. Partial sequencing followed by a computer search of data banks has shown that the cloned cDNAs correspond to mRNAs encoding proteins with extensive homology to lactate dehydrogenase, glyceraldehyde 3-phosphate dehydrogenase, enolase, triose phosphate isomerase, and actin. The complete nucleotide sequence of a rat fibroblast lactate dehydrogenase is presented.

Transcriptional regulation of a tumor promoter and mitogen-inducible gene in human lymphocytes

Tumor-promoting phorbol esters affect a variety of cellular functions which may underlie tumor promotion. We isolated from human lymphocytes a cDNA clone whose gene is inducible by the phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate as well as by the T-cell mitogen phytohemagglutinin. Nuclear transcription experiments suggested that this induction is primarily caused by the increased transcription of the gene. It is interesting that this gene is expressed constitutively in human T-cell leukemia virus-infected mature T cells. The results support the notion that 12-O-tetradecanoyl-phorbol-13-acetate can affect cellular functions by causing transcriptional activation of specific genes.

Specific stimulation of actin gene transcription by epidermal growth factor and cycloheximide

Stimulation of quiescent AKR-2B mouse embryo cells with epidermal growth factor (EGF) results in a rapid and specific induction of actin mRNA sequences. These mRNAs include those coding for both beta- and gamma-cytoskeletal, but not alpha-skeletal muscle, actin isotypes. Elongation of nascent RNA chains in isolated nuclei (run-off transcription) demonstrates that the mRNA accumulation is preceded by an increase in actin gene transcription. This increase is transient, however, and is followed by a rapid attenuation of transcriptional activity. An inhibitor of protein synthesis, cycloheximide, was also found to induce beta- and gamma-actin mRNA accumulation. Furthermore, the simultaneous addition of EGF and cycloheximide produced a synergistic effect on actin sequences in both steady-state nuclear and polysomal RNA. Run-off transcription experiments demonstrate that this synergistic effect results from an increase in the magnitude and duration of actin gene transcription. It is also specific in that alpha-tubulin gene transcription is not similarly affected. These data suggest the existence of a specific labile repressor of actin gene transcription.

Transcriptional induction of two genes in human cells by beta interferon

The binding of interferons to distinct cell surface receptors leads to the induction of synthesis of several unique polypeptides and their corresponding mRNAs (1-6). We have isolated two cDNAs that are complementary to nuclear RNA whose synthesis is induced from undetectable levels to maximal rates of transcription within 30-60 min after the addition of beta interferon to human fibroblasts or to HeLa cells. These results prove that a single polypeptide can, by binding to a specific plasma membrane receptor, promptly activate the transcription of a defined set of genes.

Transcriptional regulation of a tumor promoter and mitogen-inducible gene in human lymphocytes

Tumor-promoting phorbol esters affect a variety of cellular functions which may underlie tumor promotion. We isolated from human lymphocytes a cDNA clone whose gene is inducible by the phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate as well as by the T-cell mitogen phytohemagglutinin. Nuclear transcription experiments suggested that this induction is primarily caused by the increased transcription of the gene. It is interesting that this gene is expressed constitutively in human T-cell leukemia virus-infected mature T cells. The results support the notion that 12-O-tetradecanoyl-phorbol-13-acetate can affect cellular functions by causing transcriptional activation of specific genes.

Growth control variant cell line having increased serum requirement and decreased response to platelet-derived growth factor: reversion by 5-azacytidine

Variants of the mouse embryo fibroblast X melanoma hybrid clone 100A have been isolated by a procedure that selects against cells that are able to grow in medium containing low concentrations of serum plus insulin. Three variant clones derived from this selection were found to have a much higher serum requirement than the parental clone 100A cells, as evidenced by a very low rate of DNA synthesis and growth in medium containing low concentrations of serum. Two of the variants had approximately double the number of chromosomes as the parental cell line, while one had approximately the same number of chromosomes as the parental cells. One of the variants was very strongly reverted by 5-azacytidine but not by ethyl methanesulfonate, suggesting that it reverted by a nonmutational mechanism such as a stable change in DNA methylation. Analysis of the growth requirements in hormone-supplemented serum-free media of the 100A parent, the INS 471 variant, and revertants of the variant indicated that the variant had a specific deficiency in its growth response to platelet-derived growth factor (PDGF). PDGF dose-response curves obtained with the variant cells were shifted approximately an order of magnitude toward higher PDGF concentrations relative to PDGF dose-response curves obtained with the parental 100A cells. This quantitative increase in PDGF requirement of the INS 471 variant appears to explain the increased serum requirement of this variant. Equilibrium binding experiments performed with 125I-PDGF suggest that the variant does not have a decreased number of PDGF receptors.

Cell-cycle-specific cDNAs from mammalian cells temperature sensitive for growth

A library of double-stranded cDNA was constructed from ts13 cells, a G1-specific temperature-sensitive hamster cell line. The cDNAs, cloned into pBR322, were prepared from poly(A)+ mRNA isolated from ts13 cells 6 hr after serum stimulation at the permissive temperature of 34 degrees C. Differential screening of the library with G1-specific and G0-specific single-stranded cDNA probes prepared from the same cells identified five cDNA clones whose sequences were preferentially expressed in G1. Levels of RNA complementary to these clones were 3- to 6-fold higher in G1 than in other phases of the cell cycle. When ts13 cells were arrested in G1 at the restrictive temperature of 39.6 degrees C, the levels of RNA complementary to p13-2A9 and p13-4F1 were as high as 10 times that found in a resting population, while the expression of sequences complementary to p13-2A8 did not significantly change from levels found in G0. RNA and Southern gel blot analysis suggest that these cell-cycle-specific clones represent either low copy or moderately repetitive gene sequences. Results with another ts mutant of the cell cycle, tsAF8, which is a ts mutant of RNA polymerase II, showed that these cell-cycle-specific sequences have a rapid turnover. The use of G1-specific ts mutants of the cell cycle provides an approach to determine which cell-cycle-dependent genes are most relevant to cell cycle progression.

Nucleotide sequence of a growth-related mRNA encoding a member of the prolactin-growth hormone family

As part of the proliferative response to serum, mouse 3T3 cells produce a set of growth-related mRNAs identified by hybridization to cloned cDNAs. One of these mRNAs, which is about 1 kilobase long, appears within a few hours after stimulation of resting cells with serum or platelet-derived growth factor and reaches a high level during the transition from the G1 to the S phase of growth. This mRNA is translated in vitro into a protein of approximately 25 kilodaltons. The corresponding cloned cDNA of 791 base pairs has been sequenced; it contains a single open reading frame that encodes a protein of 224 amino acids with extensive sequence homology to mammalian prolactins. The initial 29-amino acid segment of the encoded protein resembles the signal sequences of prehormones. That the growth-related protein is not mouse prolactin is indicated by comparison of its predicted amino acid composition with that of mouse prolactin and by the distinct fragment patterns seen when restricted mouse DNA is probed with the cloned cDNA or rat prolactin cDNA. Therefore, the growth-related protein appears to be a new member of the prolactin-growth hormone family. Because of its relationship to prolactin and growth hormone and its association with cell proliferation, the protein has been called "proliferin."

Isolation of cloned cDNA encoding mammalian ornithine decarboxylase

During the growth of mammalian cells the level of ornithine decarboxylase ( OrnDCase ; L-ornithine carboxy-lyase, EC 4.1.1.17), the first enzyme in polyamine biosynthesis, undergoes rapid changes. As an initial step in the study of possible genetic mechanisms involved in these changes, we have isolated cDNA clones encoding OrnDCase . To obtain RNA enriched for OrnDCase messenger, mouse myeloma cells that overproduce OrnDCase were selected in the presence of the OrnDCase inhibitor, difluoromethylornithine. A pBR322 cDNA library was prepared from poly(A)+ RNA isolated from difluoromethylornithine-resistant cells, and the library was probed with [32P]cDNA representing mRNA sequences from resistant or parental (sensitive) cells. All clones hybridizing preferentially to the resistant cell probe shared nucleotide sequences. A representative clone containing 1.1 kilobases of cDNA was shown to encode OrnDCase sequences by in vitro translation of hybrid-selected mRNA followed by precipitation of the translation products with anti- OrnDCase antiserum. Using this cDNA clone as a probe, we found that mouse DNA yielded several restriction fragments that react with the OrnDCase cDNA. In the difluoromethylornithine-resistant myeloma cells, one of these DNA segments is amplified and the level of OrnDCase mRNA is greatly increased compared with that in parental plasmacytoma cells. The level of OrnDCase mRNA is also increased in cultured 3T3 cells stimulated with serum and in mouse kidneys after administration of androgen, indicating that OrnDCase gene transcription and/or mRNA stability are regulated during cell growth.

Analysis of male sterile mutations in the mouse using haploid stage expressed cDNA probes

A differential hybridization screening procedure has identified cDNAs which correspond to RNAs which are expressed in mouse testis and at lower levels in liver and spleen. The sensitivity of this procedure is such that approximately 0.5% of 1.4 X 10(4) cDNA clones are revealed as "testis specific". We have focused on ten cDNA clones which have been used to identify RNAs expressed in the haploid phase of spermatogenesis. Using Northern blots to analyse RNA isolated from the testes of mutant mice (Tfm/Y and Sxr/+) blocked at specific stages in spermatogenesis or RNA from sexually immature mice, 8 clones have been identified which correspond to RNAs expressed uniquely or at much higher levels in meiotic or post meiotic cells.

The role of protein breakdown in growth, quiescence, and starvation of vascular smooth muscle cells

Protein accumulation in growing cells may be due in part to a reduction in the rate of protein breakdown. Previous studies of the relation of cell proliferation to protein degradation often produced growth arrest by conditions that may involve nutritional deprivation. However, nutrient lack can itself accelerate proteolysis and produce negative protein balance. We therefore reexamined the relation between growth and protein breakdown using a more selective method for limiting cell growth. We produced quiescent cell cultures using a chemically defined, serum-free medium supplemented with hormones and nutrients. Such media can maintain viability and near neutral protein balance in cultured vascular smooth muscle cells, in part because of reduced breakdown of cellular protein. We then compared rates of protein degradation in these quiescent but not starving cells, to those of cultures stimulated to grow by addition of mitogenic substances. Platelet-derived growth factor, fibroblast growth factor, or fetuin added to insulin-containing medium stimulated growth of smooth muscle cells, but further reduced protein breakdown only slightly. Contrary to the implications of certain previous studies, our results show that proliferating cells can accumulate protein without an appreciable reduction in the rates of protein breakdown. Thus, while accelerated proteolysis appears to be an important adaptation to adverse nutritional conditions, growth of smooth muscle cells does not require changes in overall protein breakdown, but occurs primarily through an increase in protein synthesis.